This application relates to an improvement in the control of fluid flow in a surgical device. More particularly this invention relates to an improvement in the fluid flow systems for a surgical device useful in cataract removal such as that shown by U.S. Pat. No. 3,589,363 issued June 29, 1971 to A. Banko and C. D. Kelman for a Material Removal Apparatus and Method Employing High Frequency Vibrations. The aforesaid patent describes an instrument for breaking apart and removing unwanted tissue and material especially a cataract located in the anterior chamber of the eye by ultrasonically fragmenting the cataract while simultaneously introducing fluid into the eye chamber, and withdrawing the fluid and fragmented cataract particles. Briefly the device described includes a handpiece having an operative tip vibrating in the ultrasonic range which is also hollow and is in turn surrounded by a tubular sleeve. In operation the tip of the handpiece including the surrounding tubular sleeve are inserted into the anterior chamber of the eye. Treatment fluid is introduced through the hollow sleeve at a constant low pressure. This introduction of fluid which is called irrigation is to provide a replacement for fluid withdrawn or lost from the eye chamber. The withdrawl of fluid and suspended material from the anterior chamber is specifically called aspiration and ideally there is no change in fluid content or anterior chamber pressure as a result of irrigation-aspiration. This of course is impossible to achieve since aspiration is intended to remove solids which until broken up sometimes tend to occlude or block the fluid withdrawal openings of the handpiece.
This problem with control of fluid content and pressure within the anterior chamber of the eye during irrigation-aspiration is discussed in detail in U.S. Pat. No. 3,693,613 issued Sept. 26, 1972 to Charles Kelman for a Surgical Handpiece and Flow Control System for Use Therewith, and commonly assigned herewith.
A handpiece described in the aforesaid U.S. patent as well as the instrumentation described in U.S. Pat. No. 3,589,363 provides a tool tip insertable in the anterior chamber of the eye with an annular nozzle for supply of fluid for irrigation, a hollow tool tip which is vibrated at about 40,000 cps to provide the energy to break up the cataract and allow fluid withdrawl for aspirating the reduced particles and fluid. When the handpiece is inserted into the eye, it is extremely important to maintain the fluid pressure of the chamber within a certain range and to prevent rapid fluctuations of the pressure and fluid content of the chamber. A collapse of the anterior chamber for lack of sufficient pressure could result in damage to soft tissues of the eye as well as possible damage of the eye posterior capsule itself from contact of the tissues with the vibrating tool tip. This problem of maintaining the proper pressure is a particularly difficult and sensitive one and is one of the problems which the apparatus shown in the aforesaid U.S. Pat. No. 3,693,613 was designed to solve. The system shown therein while satisfactory is quite obviously a rather complex apparatus which requires in terms of control, close and competent operation personnel. Thus as part of the operation to remove a cataract from the anterior chamber of the eye the handpiece is inserted into the chamber through a small incision and the fluid flow adjusted to the desired level principally by the height at which the irrigation fluid source is supported to provide a gravity flow into the eye, and the speed of a constant flow positive displacement pump in the piping from the eye to withdraw the aspirating stream. The surgeon then moves the cataract lens into the anterior chamber, applies the ultrasonic vibration to the tip of the handpiece in contact with the lens and proceeds to break up the lens.
As part of the application of the tip to the lens the opening in the tip through which aspiration proceeds is periodically occluded by lens material. During such occlusion, fluid is prevented from entering the hollow tip, although the constant flow pump continues to operate. The pump operation thus starts drawing a vacuum in the conduit between the handpiece tip and the pump. At the same time, the pressure from the gravity feed of irrigation fluid into the eye remains constant and increases fluid pressure in the anterior chamber of the eye, expanding it somewhat. However once the opening into the handpiece tip is uncapped by fragmentation of the occlusion, the high vacuum existing in the aspirating system tends to quickly withdraw fluid from the anterior chamber. This may rapidly decompress the anterior chamber and draw the enclosing tissues towards the handpiece tip. Besides the danger represented by the ultrasonic vibrations of the handpiece tip on contact with these tissues, the rapid decompression itself may be injurious to the tissues. The apparatus shown by the aforesaid U.S. Pat. No. 3,693,613 of course is designed to eliminate such pertubrations to the eye by monitoring and controlling flow. It would be advantageous to have a system which is not only fail-safe by means of being simple rather than complex, but is also more easily regulated and controlled by normal operative personnel rather than trained technicians.